Abstract
Alkali-activated cement (AAC) is a promising binder that replaces ordinary Portland cement (OPC). In this study, the development of setting time and strength of AAC mixes were studied using ultrasonic testing method. The test results were compared with traditional Vicat setting time and compressive and flexural strengths. The findings showed that setting times and strengths have a strong correlation with ultrasonic velocity curve. The initial setting time corresponds well with the ultrasonic velocity curve’s dormant period, and the final setting time with the time it takes to reach the velocity curve’s maximum acceleration. Both setting times also showed a correlation with the value of the maximum acceleration. An exponential relation was found between the ultrasonic velocity and the compressive and flexural strengths. The effect of binder content, alkaline solid to binder ratio (AS/B), sodium silicate to sodium hydroxide solids ratio (SS/SH), and total water to total solid binder ratio (TW/TS) on the strength and setting time are also studied using Taguchi method of experimental design. AS/B ratio showed a significant influence on the setting time of AAC while TW/TS ratio showed only a minor effect. The ultrasonic velocities were able to capture the effect of the different parameters similar to the compressive strength. The velocity decreased mainly with the increase of TW/TS ratio and binder content, while AS/B and SS/SH ratios showed a lower influence.
Highlights
This is a common problem in activated cement (AAC) with ground granulated blast furnace slag (GGBS), and researches are underway to develop a suitable retarder [44,45]
Further analysis of the results showed that the maximum acceleration value varied with both the initial and final setting times
The setting and hardening process of the AAC mixture can be identified into three stages in the ultrasonic curve: the dormant stage, the acceleration stage, and the slow increase stage
Summary
Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations. Ultrasonic wave technology is a non-destructive test method that has been successfully used to monitor the setting process [18,19,20,21], compressive development [22,23], and properties such as internal defect and crack propagation of concrete [24,25] These measurements can be made continuously, providing more detailed insights into the behavior. Cao et al [26] reported the particular suitability of ultrasonic testing for AAC systems considering their quick setting and rapid hardening characteristics Despite such potential, only a few studies have been carried out on AACs. Ultrasonic wave velocity is sensitive to the formation of reaction products such as hydrates and polymers; can characterize very early microstructural changes associated with the setting process.
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